The present invention relates to an antenna element and a portable information terminal, particularly to an antenna element used in a portable telephone and a portable telephone employing such an antenna element.
As conventional antenna elements for the transmission and reception in a portable telephone, the monopole antenna and helical antenna attached so as to extend in the longitudinal direction of a casing are known.
The impedance of such antenna elements differs from the impedance of the radio transmitter-receiver in the portable telephone. Therefore, the impedance must be matched. A matching circuit to match the impedance is provided between the radio transmitter-receiver and the antenna element in the conventional portable telephone.
The matching circuit is configured by a lumped constant element such as coils and capacitors. When electric signals are transmitted from the radio transmitter-receiver to the antenna element via the matching circuit, there was a problem that a loss is generated in the coil and capacitor in the matching circuit to result in degradation of the transmission efficiency of the electric signal.
In electrical communication such as of a portable telephone, a vertically polarized wave is used as the wave to transmit information. This is due to the fact that the wave diffraction effect is great in vertical polarization. The wave can travel around a construction to arrive at the backside thereof so that a wave can be transmitted/received even to/from an area blocked by a construction.
Although the antenna element of a portable telephone is designed so as to extend substantially perpendicular in a conversation mode since a vertically polarized wave is transmitted/received as the main wave of polarization, it is known that the portable telephone terminal is generally tilted 60xc2x0 on an average to the zenith angle when used. Accordingly, there is the problem that the main wave of polarization is reversed to become a horizontally polarized wave during actual conversation.
It is therefore difficult to transmit/receive a vertically polarized wave in the practical application of a conversation mode through an antenna element that extends only in the perpendicular direction. It is particularly difficult to transmit/receive a vertically polarized wave in practical conversation when an antenna element having an electrical length which is an integer multiple of xcex/2 is used. Thus, the conventional antenna element imposes a problem that the gain in conversation is low since it is difficult to transmit/receive a vertically polarized wave during conversation in practice.
The present invention is directed-to solve such a problem.
An object of the present invention is to provide an antenna element and portable information terminal reduced in electrical signal loss and with high efficiency.
Another object of the present invention is to provide an antenna element and portable information terminal of high gain in conversation.
An antenna element according to the present invention includes a first antenna unit formed to extend in one direction, and a second antenna unit having an electrical length of substantially (xcex/2)xc3x97A (A is an integer), coupled to the first antenna unit and extending in a direction substantially orthogonal to the extending direction of the first antenna unit.
In the antenna element thus configured, the first antenna unit functions as the conventional matching circuit. Since this first antenna unit can be configured without using a lumped constant element, no loss is generated here. Therefore, the antenna efficiency can be improved. Since the second antenna unit extends substantially orthogonal to the extending direction of the first antenna element, any one of the first and second antenna units can transmit/receive a vertically polarized wave whereas the other can transmit/receive a horizontally polarized wave. Accordingly, a vertically polarized wave and a horizontally polarized wave can be transmitted/received regardless of the orientation of the antenna element. Thus, the antenna element has the gain in a conversation mode improved.
Preferably, the electrical length of the first antenna unit is approximately (xcex/4)+(xcex/2)xc3x97B (B is an integer). In this case, the first antenna unit is equal to the so-called xcex/4 antenna to reliably transmit/receive a vertically or horizontally polarized wave at the first antenna unit.
Preferably, the first antenna unit includes at least one type of antenna selected from the group consisting of a plate antenna, a monopole antenna, a helical antenna, a meander line antenna and a zigzag antenna.
Also preferably, the second antenna unit includes a line antenna.
Also preferably, the line antenna includes at least one type of antenna selected from the group consisting of a monopole antenna and a helical antenna.
Further preferably, the antenna element further includes a substrate having a conductive surface. The first antenna unit is provided on the surface of the substrate with a dielectric therebetween. The second antenna unit is provided so as to extend from the substrate.
Since the first antenna unit is provided on the substrate with a dielectric therebetween here, the wavelength of the electromagnetic wave progressing the first antenna unit can be reduced. As a result, the length of the first antenna unit can be reduced to allow a smaller antenna element. Since the second antenna unit is provided so as to extend from the substrate, a wave can be transmitted/received reliably without the second antenna unit being affected by the substrate.
Also preferably, the first antenna unit and the second antenna unit are attached in order to a feeding point.
A portable information terminal according to the present invention includes a main unit case and an antenna element. The antenna element includes a first antenna unit disposed in the main unit case and extending in one direction, and a second antenna unit arranged projectable from the main unit case, having an electrical length of approximately (xcex/2)xc3x97A (A is an integer) coupled to the first antenna unit and extending substantially orthogonal to the extending direction of the first antenna unit.
In the portable information terminal thus configured, the first antenna unit functions to match the impedance between the second antenna unit and a radio transmitter-receiver unit. Since the first antenna unit can be configured without using a lumped constant element, any loss at this region can be prevented. Since the second antenna unit extends in a direction substantially orthogonal to a first antenna unit, any one of the first antenna unit and the second antenna unit can receive/transmit a vertically polarized wave whereas the other can transmit/receive a horizontally polarized wave irrespective of the orientation of the portable telephone. As a result, a portable information terminal of a high gain in a conversation mode is provided.
Further preferably, the second antenna unit includes a third antenna unit having an electrical length of approximately (xcex/2)xc3x97C (C is an integer), and a fourth antenna unit coupled to the third antenna unit and having an electrical length of approximately (xcex/2)xc3x97D (D is an integer). When the antenna element is pulled out from the main unit case, the third and fourth antenna units project from the main unit case. When the antenna element is stored in the main unit case, the third antenna unit projects from the main unit case whereas the fourth antenna unit is located in the main unit case.
In the case where the antenna element is pulled out from the portable information terminal configured as described above, the third antenna unit having an electrical length of approximately (xcex/2)xc3x97C and the fourth antenna unit having an electrical length of approximately (xcex/2)xc3x97D project from the main unit case. Therefore, the electrical length of the projecting antenna is equal to an integer multiple of xcex/2. Accordingly, a wave can be reliably transmitted/received by this antenna. Since the third antenna unit having an electrical length of approximately (xcex/2)xc3x97C projects from the main case even when the antenna element is in an accommodated state, a wave can be reliably transmitted/received by the antenna.